Cancers and neurodegenerative disorders are often marked by dramatic changes in the expression of matrix metalloproteinases (MMPs). These proteases have been investigated as potential therapeutic targets to treat a variety of diseases. Unfortunately, with 24 different vertebrate MMPs, clinical trials have been hindered by side effects, suggesting that MMPs are important for normal physiological functions. There are only two MMPs in Drosophila, making it an excellent model system to study MMP function as the problems of redundancy and compensation are largely eliminated. We recently reported that Drosophila MMPs are important for the fasciculation/bundling of axons during embryonic development. To understand Frac function during neuronal development, it is critical to identify its proteolytic substrate(s). A candidate target, Fatal Attraction (Frac), has been identified in a yeast two-hybrid screen. In this proposal, we propose to characterize the function of Frac in axon guidance and determine whether it is regulated by Mmp2. Frac protein is homologous to the vertebrate Matrilin and Fibrillin protein. Loss of fibrillin in humans leads to Marfan or Beals syndrome indicating that these studies are likely to be relevant clinically. Preliminary results indicate that frac RNA is localized to embryonic muscle, a position consistent with a role in axon guidance. Frac misexpression in muscle results in axon guidance defects that are indistinguishable from the defasciculation phenotype reported in Mmp2 loss-of-function (LOF) mutants strongly supporting a functional link between Frac and Mmp2. We hypothesize that Frac acts as an adhesive molecule in muscle to attract axons to their target muscles and away from nerve branches. Mmp2 would then be responsible for cleaving and inactivating Frac. In Specific Aim 1, we will characterize the function of Frac in axon guidance by assaying the frac LOF mutant phenotype and genetic interactions between frac and Mmp2. Specific Aim 2 tests whether Frac is processed and, if so, whether this cleavge is Mmp2-dependent. As this proposal addresses the characterization of a novel Mmp2 substrate likely involved in axon guidance decisions, it may shed light on the normal physiological functions of MMPs and their substrates in vertebrate neuronal development.